Thanks for your reply.
You may check within the following section of your theme options; Appearance>Theme Options>Header>Header Background Header Top & Bottom Padding and make sure they are set to 0.
You may use the following Custom CSS Code to accomplish this request.
/*Reduces the Top & Bottom Padding to Reduce the Header Height*/
padding-top: 20px !important;
padding-bottom: 0 !important;
Please let me know if there are any more questions that I can answer for you 🙂